Sir -- In his Jan 27 commentary, Nick Priest 1 discusses the radiotoxic effects of depleted uranium. We calculated the radiation doses to gunnery range staff and local residents that might arise from the testing of depleted uranium munitions at the Eskmeals range, which is located near to our institute.

We took account of published data on the total mass of depleted uranium in shells tested at the range over the past few years (equivalent to 170 shells, each with an average depleted uranium content of 5·4 kg per year). We calculated the expected radiation doses to a hypothetical member of the range staff who was standing 50 m from the target during each and every firing. We also calculated expected doses to the nearest local residents, assumed to be 500 m from the target. We assumed that 20% of the uranium content of each shell was dispersed as a fine aerosol with a mean aerodynamic diameter of 1 µm.

Our calculated radiation dose (committed effective dose) to the hypothetical member of range staff was 20 µSv (microsieverts) per year, not 20 mSv (millisieverts) per year as stated in the commentary, compared with an average dose from natural background radiation in the UK of 2200 µSv per year. For the local residents, the calculated dose was only 2 µSv per year. The corresponding risks of developing a fatal cancer are about one in 1 million and one in 10 million for range staff and residents, respectively.

The calculations lend force to Priest's conclusion that any conceivable uptake of depleted uranium will not have carcinogenic potential. However we welcome the investigations into exposures of servicemen and service- women that have been started.

*Steve Jones, Ian Lowles, Andy Smith
Westlakes Research Institute, International Research and Graduate Centre, Westlakes Science and Technology Park, Cumbria CA24 3JY, UK

We informed Medical Action for Global Security about this effect in 1999, and the Royal Society depleted uranium panel in 2000. Animal experiments2 and human necropsies 3 have shown that tracheobronchial lymph nodes can retain high concentrations of actinides. Clearance of insoluble oxides is slow.

We calculate that a particle 0·5 µm in diameter delivers chronicirradiation to local tissue ten times the natural background rate. ß rays from daughter isotopes are additional; larger particles would deliver higher doses, but adjustments should be made for self-absorption.

The methods of the International Commission on Radiological Protection (ICRP) for calculating doses do not take account of this type of exposure. They assume that the averaging of the energy deposition across entire organs is valid. On this basis, depleted uranium confers very low radiation doses. However, respected academics have said that at low doses, the term dose should be dropped and fluence of charged particles through the tissue be referred to. According to this suggestion, conventional dose terms are valid only when all the cells in a volume of tissue have been hit at least once.

The ICRP model is based on studies of the mutagenic effects of the single acute externaldose experienced by survivors of the Hiroshima and Nagasaki bombs. The control group for these studies was people who lived in the bombed cities and who, therefore, had equal exposure to inhaled and ingested fallout. The very small amount of information on internal irradiation that moderates the ICRP model includes no man-made isotopes nor the anthro-pogenic type of exposure created by the impact of depleted uranium weapons.

Busby 4 has drawn attention to this deficiency with especial reference to hot particles. Press reporting of the depleted-uranium controversy includes comments by Dudley Goodhead and Eric Wright on how uranium particles in lymph nodes might damage stem cells, possibly inducing leukaemia and genomic instability.

The uranium content of the lymph nodes of populations exposed to depleted-uranium dust must be measured before any conclusions on the health effects can be reached.

Richard Bramhall
Low Level Radiation Campaign, Llandrindod Wells, Powys LD1 5LW, UK
(e-mail:bramhall@llrc.org)

2 Leach LJ, Elliott AM, Hodge HC, et al. A five year inhalation study with natural uranium dioxide dust, 1: retention and biological effect in the monkey dog and rat. Health Physics 1970; 18: 599-612. [PubMed]

3 McKinroy JF, Kathren RL, Voelz GL, Swint MJ. US Transuranium Registry Report on the 239 Pu distribution in a human body.Health Physics 1991; 60: 307-33. [PubMed]

4 Edwards AA, Cox R. Commentary on the Second Event Theory of Busby.Int J Radiat Biol 2000; 76: 119-25. [PubMed]